5.5.12  Read a float from a string

Read a float from a string:

    f = atod "2.3";

Read a float from a string, II:

    f = float::from_string "2.3";

Read a float from a string, III:

    eval:  sscanf "12.3" "%f";

    THE [FLOAT 12.3]

    eval:  scanf::sscanf "12.3" "%f";

    THE [FLOAT 12.3]